The present invention relates to a drilling machine arrangement and, more particularly, to a drill chuck arrangement which connects a drill bit to a spindle on a drilling machine.
Hand-held drilling machines for working on stone, concrete and similar materials are provided, to an ever-increasing extent, with an adapter which can convert the pure rotary movement of a rotating spindle to a pure axially directed impact-type movement or to a combination movement having both rotary and axial components of motion. The back-and-forth axial movement loosens the connection between the drill bit and the clamping jaws, and therefore requires a relatively firm clamping force.
In one known chuck or clamping jaw attachment, three jaws are provided in a spindle member. The jaws have threads which thread into a guide sleeve. By turning the sleeve with a tool, the jaws are displaced in a direction transverse to the turning axis, and thereby clamp or release a drill bit inserted in between the jaws. However, the jaws of this prior art arrangement have a tendency to automatically open and release the drill bit, especially in impact-type drilling having an axially directed component of motion.
In another known so-called quick-connect chuck used in impact-type drilling, a spindle member is screwed onto the spindle of a drilling machine. A guide member is turnably mounted on the spindle member and is provided with three jaws transverse to the turning axis. The guides for the jaws are surrounded by a guide sleeve which is screwed on the guide member. The rear end of each of the jaws has a radially aligned T-shaped extension which cooperates with a corresponding T-shaped groove of a displaceable member. The displaceable member has a threaded pin at its rear end which is threaded into a left-handed thread provided on the spindle member. In addition, this chuck has a holding ring threaded onto the guide member which prevents the latter from being detached from the spindle member.
This latter prior art chuck clamps a drill bit inserted in between its opposed jaws essentially more firmly than the earlier described three-jawed chuck because of the presence of the left-handed thread connection between the spindle member and the displaceable member. However, this chuck has the disadvantage that it is simple to open because the force required to turn the guide member relative to the spindle member is generated manually. A drill bit is thereby held with a relatively weak clamping force.
Moreover, this chuck has the further disadvantage that it is subject to binding and seizing. The guide member directly engages the spindle member so that they are prone to binding together, thus presenting a considerable force which prevents the jaws from opening, as desired.